A total of 30 surgically resected complete mitral valves were examined, without prior knowledge of the clinical history, to evaluate the reliability of gross inspection only for the correct morphological diagnosis. Twenty valves were rheumatic; 10 were obtained from patients with idiopathic mitral valve prolapse. Two groups were identified: group I correlated with a rheumatic history; group II showed floppy mitral valves, which correlated with mitral valve prolapse. Hence, it is considered that the diagnosis of rheumatic or floppy mitral valve can be established accurately upon gross examination only. The rheumatic valve is fibrotic and firm, leading to thickening and fusion of leaflets and commissures. Narrowing and lowering of the "principal" ostium occurs. This results in a funnel-shaped valve, which is further accentuated by interchordal fusion. Rigidity is its hallmark. Chordal rupture is unlikely. Calcification can be found anywhere in the valve. Hooding is extremely unusual. The floppy valve, by contrast, shows laxity of leaflets, which may lead to the formation of dome-like deformities reaching above the level of the annulus. The chordae are often thin, attenuated, and may have ruptured. The distribution of chordae and mode of anchoring is often chaotic. Fibrosis occurs mainly at the anchoring sites of the chordae underneath or at the margin of the leaflet, or where previously ruptured, intertwined chordae are plastered underneath the dome. Fibrosis is further aggravated at the margins and atrial surface of the leaflets because of regurgitant friction. In spite of fibrosis, the floppy valve remains soft and flexible. Commissural fusion is absent. Interchordal fusion is not a characteristic feature of the floppy mitral valve. Gross inspection will not only correctly discriminate between a rheumatic and floppy mitral valve, but may also contribute to an understanding of the pathogenesis of the valve deformity.